Quote, It's an 85 Ah battery so 80% would mean it needed 17 Ah to reach full charge (actually more like 20 Ah due to losses). Even allowing for the fact that an old battery won't really be 85Ah, it takes vastly less than 20Ah to reach full charge I'd say more like 4 or 5 Ah at the most. So the 80% figure in my case is more like 90% or higher depending on the batteries real capacity. Quote.
It all depends on the state of the battery, how the car is driven and how many miles per year, if there is a lot of braking or coasting down hill the battery will receive more charge.
Regenerative braking is only effective if the starter battery has some spare storage capacity to absorb the charge created by the alternator during deceleration. If the starter battery was fully charged the electrical energy created would be wasted and so the ECU aims to maintain the battery at around 80% state of charge (low enough to have spare storage capacity but high enough to guarantee engine starting if required).
Aux Battery Charging With Smart Alternators | 12 Volt Planet
It all depends on the state of the battery, how the car is driven and how many miles per year, if there is a lot of braking or coasting down hill the battery will receive more charge.
Regenerative braking is only effective if the starter battery has some spare storage capacity to absorb the charge created by the alternator during deceleration. If the starter battery was fully charged the electrical energy created would be wasted and so the ECU aims to maintain the battery at around 80% state of charge (low enough to have spare storage capacity but high enough to guarantee engine starting if required).
Aux Battery Charging With Smart Alternators | 12 Volt Planet
Yes I understand the theory and why they do it. 80% is always quoted as the figure when smart alternators are described but I'm seeing in practice that my battery is being maintained at more than 80%. I know that the smart function is working because I've monitored voltage changes on the move.
If it really was universally as low as 80% then I'd expect to see owners experiencing a noticeable reduction in battery life and there doesn't seem to be any evidence of that.
If it really was universally as low as 80% then I'd expect to see owners experiencing a noticeable reduction in battery life and there doesn't seem to be any evidence of that.
quote So you disconnected the battery sensor so that Stop/Start never kicks-in (i.e. instead of having to disable it by pressing the bottom at the start of every journey)? Quote.
Then you forget to press the button and try to floor it out of a busy junction, that small unexpected hesitation is rather scary I can assure you. I think folks will find that keeping stop/start functioning will cost far more than any savings gained on fuel, if there is little or no fuel savings there is no point in stop/start, its just another layer of electronics to go wrong, it does enable the manufacturer to increase prices though.
Then you forget to press the button and try to floor it out of a busy junction, that small unexpected hesitation is rather scary I can assure you. I think folks will find that keeping stop/start functioning will cost far more than any savings gained on fuel, if there is little or no fuel savings there is no point in stop/start, its just another layer of electronics to go wrong, it does enable the manufacturer to increase prices though.
Quote If it really was universally as low as 80% then I'd expect to see owners experiencing a noticeable reduction in battery life and there doesn't seem to be any evidence of that. Quote.
Look at the thread.
Johnson Controls, the world’s largest start-stop battery manufacturer, told BESB on August 10 that ‘parties’ were discussing the complete removal of the option to override the start-stop function in new cars.
Another global lead battery manufacturer that asked not to be named also said it “does believe there will eventually be a requirement to remove the choice of using start/stop in the vehicle given its use is directly tied to CO2 emissions and fuel economy standards”.
Although there is no legislation that orders OEMs to remove the override function, some carmakers are already making the option more and more obscure, Christian Riedel, director of communications EMEA for JCI, told BESB.
Aftermarket growth in AGM and EFB batteries used in start-stop vehicles has failed to meet predictions because the batteries are being under-used by drivers who choose to switch off the start-stop function in their vehicles, said John Bentley, technical spokesman of Ecobat Technologies (formerly Manbat).
“The fundamental issue comes down to the fact that the AGM batteries developed to cope with the demands of these start stop systems are, in practice, not being used in the way they were designed,” he said.
AGM aftermarket falters as drivers disable start-stop function - Batteries International
Look at the thread.
Johnson Controls, the world’s largest start-stop battery manufacturer, told BESB on August 10 that ‘parties’ were discussing the complete removal of the option to override the start-stop function in new cars.
Another global lead battery manufacturer that asked not to be named also said it “does believe there will eventually be a requirement to remove the choice of using start/stop in the vehicle given its use is directly tied to CO2 emissions and fuel economy standards”.
Although there is no legislation that orders OEMs to remove the override function, some carmakers are already making the option more and more obscure, Christian Riedel, director of communications EMEA for JCI, told BESB.
Aftermarket growth in AGM and EFB batteries used in start-stop vehicles has failed to meet predictions because the batteries are being under-used by drivers who choose to switch off the start-stop function in their vehicles, said John Bentley, technical spokesman of Ecobat Technologies (formerly Manbat).
“The fundamental issue comes down to the fact that the AGM batteries developed to cope with the demands of these start stop systems are, in practice, not being used in the way they were designed,” he said.
AGM aftermarket falters as drivers disable start-stop function - Batteries International
Oli74
New Member
I have the same problem, stop/start is selected (green light on near central console) but the light on the dashboard has remained yellow for a while now. I understand there are a few conditions to be met for the function to work...but I was wondering if it has stopped working since I hardwired a dashcam which I connected it to a permanent positive (using Nextbase hard wire kit which has a low battery safety feature) and maybe it drains the battery just a little bit too much?
I have read from this forum that the car (c220d 2016 model amg line) has 2 batteries, should I have used a different permanent positive? I used the fusebox next to the steering wheel, the one you access by removing the panel with the door open). I could take it for a diagnostic as the car is under warranty but they might charge me saying I caused it due to the hardwiring...
I have read from this forum that the car (c220d 2016 model amg line) has 2 batteries, should I have used a different permanent positive? I used the fusebox next to the steering wheel, the one you access by removing the panel with the door open). I could take it for a diagnostic as the car is under warranty but they might charge me saying I caused it due to the hardwiring...
Oli74
New Member
HOLD does work. Any link with the hardwiring I have done?
400ixl
MB Enthusiast
Which battery is the circuit you have hard wired on? Simple test is to remove the wiring and see if it corrects the problem.
Oli74
New Member
Not sure what battery I connected to, I just found a permanent 12v with the voltmeter. I will have to check the fuse diagram. Meanwhile I will probably try to disconnect and see if the stop/start goes green again.
D
Deletedmember130310
Guest
If you need to make that quick a get away, the gap is probably too tight and you shouldnt be proceeding.
Ted
MB Enthusiast
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Yellow = turned on but at least one condition for stop/start not met. (Eg engine temp, battery voltage/condition etc)
Green = turned on all conditions for stop/start met.
Green = turned on all conditions for stop/start met.
Oli74
New Member
Car is back from the dealership, found a faulty bonnet sensor that stopped it from working!
Hi, recently bought a used GLC 250D from a main dealer (late 2017 model but with only 6000 miles it's like a brand new car
) and am really pleased with it save for one irritating thing.....
The stop-start system does not seem to be working as it should....operation has been somewhat erratic (!!) since purchase a few weeks ago
e.g.
Yesterday I drove about 8 miles - it did not operate once and the dash light was yellow. I parked up and went into a shop, about 15 mins later I drove home and from start the dash light was green all the way with S/S operating as it should.
Some 4 hours later (with the engine still amazingly close to operating temperature!) I drove about 18 miles and the light was yellow with no S/S operation all the way, 1/2 hour later I drove home and it worked initially (green light) but after about 10 mins went yellow again and remained so for the rest of the journey.
Today I drove about 10 miles......after 1/2 mile the temp gauge showed 60 deg C (must say it warms up impressively quickly), the S/S light went green and remained so for the whole journey, S/S worked as it should.
Came out of the shop after may be 10 mins, started the car and the light was yellow.......and remained so for the whole journey home .....with, of course no stop start......
I appreciate there are many factors that govern it's operation but the air-con had very little load (o/s temp 21, inside set at 20 and the blower fan was barely running, I tried turning off the air-con just in case but it made no difference
So, the engine is at operating temp, there is no condensation or humidity present in the car, the battery is presumably fully charged by now .............and as the engine starts within 1/2 sec, a few starts are hardly going top drain the battery
None of my previous cars (including a 2012 E-class 250D) have suffered this problem and I am really disappointed that such a new car from such a prestige marque is doing so, the dealer has been helpful and suggested the battery may not have been fully charged after sitting in their sales yard so they took the car back to charge the battery fully....after which it worked for a day
I have also trickle charged the battery for 2 days at 14.5V on a stabilised and regulated lab. class power supply and the next day it worked as it should, the day after it didn't.
The (engine running voltage) at the battery is around 14.6 to 14.8 which to ME seems rather high, even after fully charging it myself - I would have expected a lower voltage with a fully charged battery.
Ideas and suggestions welcomed, unlike some people on the forum I WOULD like this to work and cut the engine whenever possible.,...I do after all always have the option of turning it off !thanks
The stop-start system does not seem to be working as it should....operation has been somewhat erratic (!!) since purchase a few weeks ago
e.g.
Yesterday I drove about 8 miles - it did not operate once and the dash light was yellow. I parked up and went into a shop, about 15 mins later I drove home and from start the dash light was green all the way with S/S operating as it should.
Some 4 hours later (with the engine still amazingly close to operating temperature!) I drove about 18 miles and the light was yellow with no S/S operation all the way, 1/2 hour later I drove home and it worked initially (green light) but after about 10 mins went yellow again and remained so for the rest of the journey.
Today I drove about 10 miles......after 1/2 mile the temp gauge showed 60 deg C (must say it warms up impressively quickly), the S/S light went green and remained so for the whole journey, S/S worked as it should.
Came out of the shop after may be 10 mins, started the car and the light was yellow.......and remained so for the whole journey home .....with, of course no stop start......
I appreciate there are many factors that govern it's operation but the air-con had very little load (o/s temp 21, inside set at 20 and the blower fan was barely running, I tried turning off the air-con just in case but it made no difference
So, the engine is at operating temp, there is no condensation or humidity present in the car, the battery is presumably fully charged by now .............and as the engine starts within 1/2 sec, a few starts are hardly going top drain the battery
None of my previous cars (including a 2012 E-class 250D) have suffered this problem and I am really disappointed that such a new car from such a prestige marque is doing so, the dealer has been helpful and suggested the battery may not have been fully charged after sitting in their sales yard so they took the car back to charge the battery fully....after which it worked for a day
I have also trickle charged the battery for 2 days at 14.5V on a stabilised and regulated lab. class power supply and the next day it worked as it should, the day after it didn't.
The (engine running voltage) at the battery is around 14.6 to 14.8 which to ME seems rather high, even after fully charging it myself - I would have expected a lower voltage with a fully charged battery.
Ideas and suggestions welcomed, unlike some people on the forum I WOULD like this to work and cut the engine whenever possible.,...I do after all always have the option of turning it off !thanks
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The most common reason for Stop/Start issues is either the main battery or the auxiliary battery.
The batteries are electronically controlled and the Stop/Start ECO could decide that they are not OK even if to the naked eye they seem fine.
And, the issue could also be with one of the components in the battery management system (i.e. not the actual battery itself).
There are other possible causes, but they will show on STAR. A poor battery won't show on STAR and the only way to eliminate it is by replacing both batteries (one at a time).
Said that, with your car being still under warranty, take it to dealer, and insist that they keep the car until they fix the issue. The Stop/Start should green about 80% of the time, more so on Motorways.
PS - when the engine is running, the voltage is not determined by the battery, but by the alternator and voltage regulator.
The batteries are electronically controlled and the Stop/Start ECO could decide that they are not OK even if to the naked eye they seem fine.
And, the issue could also be with one of the components in the battery management system (i.e. not the actual battery itself).
There are other possible causes, but they will show on STAR. A poor battery won't show on STAR and the only way to eliminate it is by replacing both batteries (one at a time).
Said that, with your car being still under warranty, take it to dealer, and insist that they keep the car until they fix the issue. The Stop/Start should green about 80% of the time, more so on Motorways.
PS - when the engine is running, the voltage is not determined by the battery, but by the alternator and voltage regulator.
grober
MB Master
Either the main battery or the auxiliary battery or both have a fault- sounds as if one or more of them is failing to hold charge- this will be as a direct result of sitting for some time in a discharged state-- long enough to drastically reduce the batteries charge capacity and probably irrecoverable . This may have occcured on the dealers lot or bearing in mind the low mileage at several times in its past ownership . Simplest solution is to get them to renew both batteries under warranty and take it from there--- I see Markjay got there first! the main battery is the one that does the "heavy lifting"= starting calling the auxilliary battery the "stop start battery" 
is misleading -it never plays a part in starting the engine it merely maintains the cars vital electrical systems while the engine is temporarily stopped - when called to start again its the main battery that does this
is misleading -it never plays a part in starting the engine it merely maintains the cars vital electrical systems while the engine is temporarily stopped - when called to start again its the main battery that does this
Last edited:
c63chris
MB Enthusiast
Those symptoms are exactly what I had and it was the battery. Battery changed and all back to normal. There is a difference between having enough charge so the cars systems seem to work ok and the stop/start allowing itself to function. I wasn’t convinced but it was done under warranty and to be fair has worked fine ever since
